This invention relates to precision control and/or measurement of location of a movable element in relation to a fixed point, and more particularly to the achievement thereof using time interval measurement techniques applied to an elongated magnetostrictive rod or other energy propagative member affording a basis for manual or electrical control and/or remote indication and control of the movable element's position. The invention is herein illustratively described in its presently preferred embodiment suitable, for example, to control positioning of a film or print strip in relation to a cutter used in commerical photographic film processing laboratories in cases where the strip is not pre-notched or otherwise marked as a basis to time the operation of the cutter as a function of strip feed position. However, it will be evident that the invention is applicable in other forms and to other uses without departure from its essential features.
Certain problems in precision distance measurement using energy propagation members include problems arising from attempts to terminate the member at one or both ends in its characteristic impedance so as to avoid energy reflections. An object hereof is to circumvent these difficulties and in fact to employ terminations that produce reflections, primary ones of which (first in time) are utilized in the time interval measurement process.
Still other problems imposing restriction on measurement accuracy have indirectly to do with end reflections in the propagative member, but more especially to sensing transducer placement which will yield unambiguous and accurate wave energy sensing responses without an unduly critical positioning requirement as regards forming and locating the sensing transducer along the member. A further object hereof, therefore, is to overcome such difficulties in an improved locating apparatus, and one which is capable of ignoring or rejecting from its sensing transducer responses both spurious signals and responses attributable to ringing effects in the member, that is attenuated energy reflections occurring subsequent to those first two response signals actually employed in the measurement logic implementation.
Still another objective hereof is to provide such a system that automatically compensates for changes in shock wave propagation velocity in the member attributable to ambient temperature or other effects that otherwise disturb the calibration based on propagation time interval between fixed points along the member.
In accordance with another object of this invention, program logic and a digital counting system controlled thereby, provide time interval measurements digitally indicating movable element position with a high degree of precision. Furthermore, it is an object to achieve the same degree of precision using digital circuit elements common to those used in the basic measurement, to provide continuing (i.e. cycle-to-cycle) compensation for changes in shock wave propagation velocity in the member.
These and other objectives and advantages of the invention, including its inherent simplicity, ease of practical manufacture and operation, versatility for various uses and in varying forms will become evident from an understanding of its preferred embodiment hereinafter disclosed.